1. Field of the Invention
This invention relates to lead-acid cells and, more particularly, to sealed, maintenance-free, lead-acid cells suitable for use in rapid recharging applications.
2. Description of the Prior Art
Sealed lead-acid stationary batteries are widely used in commerce today. Stationary batteries are specifically designed for float applications, that is, as standby power in the event of a power failure. Stationary batteries are maintained at a full state-of-charge and in a ready to use condition, typically by floating at a constant preset voltage. Stationary batteries are used for standby or operational power in a wide variety of applications, including, by way of illustration, in telecommunications, utilities, for emergency lighting in commercial buildings, as standby power for cable television systems and in uninterruptible power supplies.
The sealed lead-acid stationary batteries used for industrial applications where the power requirements are high and quite demanding are typically comprised of from several to a large number of individual sealed lead-acid cells connected to one another to form a battery with the desired capacity and power requirements. The individual sealed lead-acid cells may be connected in series, in parallel or in suitable combinations of series and parallel to form a battery with the desired capacity and power requirements. External connections are typically made between the negative and positive terminal posts of the respective cells.
In presently available sealed lead-acid cells, both the positive and the negative terminals are located at the same end of the cell. Accordingly, in order to externally connect a plurality of cells to form a battery, intercell connections of varying length are required, whether the cells are connected in series, in parallel, or in some combination of series and parallel. Because of the different lengths of the intercell connectors, the resistance across the connectors will vary. It would be beneficial to be able to connect a plurality of sealed lead-acid cells with a uniform size intercell connector for expediency, efficiency and economy in arranging and assembling the cells into a battery and to minimize the resistance of both the intercell connection and the battery.
The sealed lead-acid cells that comprise the stationary batteries employed in large industrial applications are typically quite large and require substantial space merely to accommodate the battery. The enormous size of such batteries is due in large measure to the large physical size of the individual cells which comprise the battery and the large number of cells that are typically needed to construct a battery having the required capacity and power requirements. It would be desirable to provide sealed lead-acid cells having a greater energy density and greater capacity per unit volume than presently available sealed lead-acid cells to reduce the number of cells required to supply the requisite power and to reduce the overall space requirements of the battery.
When stationary batteries are put into service, as, for example, when there is a power interruption, the batteries are often subjected to a heavy load, and thus, rapidly discharge. When the battery is placed on discharge, the voltage of the battery initially drops abruptly due largely to the resistance of the battery. As the discharge proceeds, the rate at which the voltage decreases is slower due to the fact that the reactive materials in the battery, i.e., the active materials in the plates and the sulfuric acid are reacting. Toward the end of discharge, the voltage falls more abruptly as the sulfuric acid of the electrolyte and/or the active materials on the plates become depleted so that they can no longer support the rate of discharge. When the battery and thus cells are placed on a high rate of discharge, as for example when large current is required in the event of a power outage and the battery is engaged to supply the requisite power, the resistance is important to the overall performance of the battery.
According to Ohm's Law, the total voltage drop on discharge includes both the voltage drop across the terminals of the appliance to be powered and the internal resistance of the battery. For stationary batteries comprised of a plurality of cells, the internal resistance of the battery is the combined resistance attributed to the internal resistance of the individual cells and the resistance across the intercell connectors. The power loss of the cells (and thus of the battery) increases with the square of the current. Resistance is expended in heating the cells and battery, and is lost. Particularly, then, at high rates of discharge, the watt-efficiency of the battery is reduced, and the useful power that the battery can give is limited.
It would be desirable, therefore, to provide sealed, lead-acid cells suitable for use in stationary batteries, capable of enduring deep discharge and rapid recharging and having a long cycle life, increased capacity, and reduced combined resistance. It would also be desirable to provide such cells which can be connected together to form a battery with a minimum and uniform-sized intercell connector to minimize resistance in the intercell connection.
Accordingly, a principal object of the present invention is to provide a sealed lead-acid cell capable of enduring deep discharge and rapid recharging, having a long cycle life and which is suitable for use in stationary batteries.
It is a further object of the present invention to improve the energy density of a sealed lead-acid cell. It is a related object to reduce the internal resistance of such a cell. It is a further object of the present invention to provide a cell in which the head space is reduced and taller plates can be used for a cell of predetermined size.
Yet another object of the present invention is to provide a sealed lead-acid cell which, when assembled into a battery, has reduced space requirements. It is a more specific object of the present invention to provide a sealed lead-acid cell that is physically smaller than currently known sealed lead-acid cells of comparable capacity.
It is another object to provide a sealed lead-acid cell which provides for a relatively direct current path for the removal of current from the cell. It is a related object to provide a cell in which the current path from the plate lugs to the post is relatively short for both the positive and negative plates. It is another, more specific, object of the invention to provide a direct current path from the lugs to the terminal post, and to eliminate the strap, post and post burn.
It is another object of the present invention to provide a sealed lead-acid cell in which the positive and negative terminals are disposed at opposite ends of the cells. It is a related object of the invention to improve the utilization of the electrode active material of the positive and negative plates. It is a more specific object to improve the utilization of electrode active material over the total area of the plates.
It is also an object of the present invention to provide sealed lead-acid cells which are capable of being connected either in series, or in parallel, or in a combination of series and parallel with a uniform-sized intercell connector. A related object is to provide a battery comprised of a plurality of sealed lead-acid cells in which the length of the intercell connector is minimized.
A further object of the present invention is to provide a sealed lead-acid cell which includes means for pre-aligning the plate lugs before the plate lugs are electrically coupled. It is a related object to provide pre-aligning plate lug means which is capable of preventing lead run-down into the plates.
It is a more specific object of the present invention to provide a high power density, sealed lead-acid recombinant cell.
These and other objects and advantages of the present invention will be apparent from the following description and drawings.